1. Field of the Invention
The invention relates to a lens testing device and method, and more particularly, to a lens testing device and method for a plurality of object distances.
2. Description of the Related Art
Presently, lenses have been extensively applied to various kinds of mobile devices, such as cellular phones, mobile devices and digital cameras. During the manufacturing processes, qualities of lenses are subject to change due to process deviations. Therefore, the lenses need to be tested before shipping to ensure that the finished lenses meet specifications of an original design. For example, lens test at least include the following categories: an optical lens test of reciprocal projection for a finite distance, an optical lens test of reciprocal projection for an infinite distance, an optical lens test of orthographic projection for an infinite distance, and an optical lens test of orthographic projection for a finite distance.
FIG. 1A shows a diagram of a conventional lens testing device for testing a lens. A lens testing device 100a is used to test the quality of a finite-distance lens. The testing method is to place a photo sensor (such as an image sensor) at a field of view (FOV) or an angle required for testing an optical lens or an imaging system, and to perform a test for a fixed object distance so that the optical quality of the finite-distance lens is measured. Referring to FIG. 1A, the lens testing device 100a includes at least an image sensor 110, a lens under test 120 and a test graphics projection module 130. The test graphics projection module 130 includes a light source 131 and a test pattern 132. The light source 131 emits a light beam passing the test pattern 132 to form a patterned light beam. Here, different test patterns 132 can be used for different characteristics of the lens under test 120. During the test, the light beam from the light source 131 illuminates the test pattern 132 to generate the patterned light beam, and then the patterned light beam passes the lens under test 120 to illuminate the image sensor 110. The image sensors 110 capture an image and transfer the image to a host computer 150. Then, the host computer 150 analyzes the captured image to obtain the following information, such as a resolution, an opto-electronic conversion function (OECF), a grayscale, a modulation transfer function (MTF), and spatial frequency responses, or the like.
FIG. 1B shows a diagram of another conventional lens testing device for testing a lens. A lens testing device 100a is able to test the quality of an infinite-distance lens by adding a telescope 140 in front of each photo sensor (such as an image sensor) and placing the telescope 140 at a field of view (FOV) or an angle required for testing an optical lens or an imaging system so that a test image is simulated to form an image at an infinite distance, thereby achieving the purpose of testing an object at an infinite distance. More specifically, referring to FIG. 1B, the lens testing device 100b further includes at least a telescope 140. The light source 131 emits a light beam passing the test pattern 132 to form a patterned light beam. Here, different test patterns 132 can be used for different characteristics of the lens under test 120. During the test, the light beam from the light source 131 illuminates the test pattern 132 to generate the patterned light beam, and the patterned light beam is simulated by the telescope 140 to form an image at the infinite distance. Then, the patterned light beam passes the lens under test 120 to illuminate the image sensor 110. The image sensors 110 capture an image and transfer the captured image to a host computer 150 for analysis. Techniques regarding an optical lens test of orthographic projection for a finite distance and an optical lens test of orthographic projection for an finite distance are similar to an optical lens test of reciprocal projection for a finite distance and an optical lens test of reciprocal projection for an infinite distance. In general, their differences are different positions of the image sensor 110 and the test graphics projection module 130. The above-mentioned techniques are well known in the art and thus detailed description is omitted for the sake of brevity.
When a video conference or an autodyne is performed by a cellular phone, a shooting distance between a lens of a cellular phone and a subject is usually less than an arm's length, which is around 400˜600 mm. When a cellular phone is used to shoot a landscape scene, the shooting distance between the lens and the landscape is more than two meters or even farther. Therefore, the best solution is to test a lens for both a finite object distance and an infinite object distance to determine the quality of the lens.
However, as mentioned above, the lens testing device 100a or 100b performs an optical test for either the finite object distance or the infinite distance without a comprehensive consideration of the demand of a plurality of working distances.